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Genuine GM parts have one of these marks:

Vehicle Care
California Proposition 65 WarningMirrors
Specifications
Inside Rearview Mirror Schematics
Outside Rearview Mirror Schematics
Outside Rearview Mirror Replacement
Preliminary Procedure
Remove the front side door trim. Refer to Front Side
Door Trim Replacement.
Remove the front side door upper trim cove ...
How To Indentify Plastic Parts
Plastic parts can be identified by the SAE code, which is usually found on
the rear of the part, and/or by the characteristics of the plastic.
Knowing the type of plastic aids in selecting the proper repair materials and in
selecting the proper repair procedure.
Look for the SAE code s ...
Installation Procedure
Align the body side outer panel reinforcement.
Clean and prepare the attaching surfaces for welding.
Position the body side outer panel
reinforcement on the vehicle.
Verify the fit of the body side outer panel reinforcement.
Clamp the body side outer panel reinforcement ...